The recently published 'ovs' theme [1] copies the styling of the Open
vSwitch website. Start using this, with fallbacks for users who do not
have the package installed.
This extends support for building docs to users of Sphinx 1.2 as the
previous theme - bizstyle - was only available in 1.3+.
[1] https://pypi.python.org/pypi/ovs-sphinx-theme
Signed-off-by: Stephen Finucane <stephen@that.guru> Signed-off-by: Ben Pfaff <blp@ovn.org>